To predict and confirm the frequency characteristics and time-domain performance of the fast steering system (FSM) in the structural design stage, a two-axis flexible-supported FSM was studied and tested. A new flexible support structure was proposed, and the main structural parameters of the FSM system were designed based on the performance index of FSM which is decided by the beam requirement of laser transmission system. The dynamic mathematical model of the system was studied, and the control mode and parameters of the closed-loop system were determined. The rigid-flexible coupling model of the swing part of the system was established, and the structural non-linear model was obtained. The joint simulation test of the system and the motion system were carried out based on the model above. The simulation results show that the resonance frequency of the system in the direction of motion is 54 Hz, and the errors between the calculated result and the finite element result is both 3.8%, and position closed loop bandwidth is 203 Hz which is right to the index. The output results in time domain show that the overshoot of the system is 3.5% and the adjustment time is 10 ms, the deviations from the theoretical results are 3% and 5 ms.